E.g. the G2 imagemagick module does not work if you have not installed the ImageMagick binaries on the webserver. Binaries in this context are executable files that start a program. You can download precompiled binaries for most of these modules from the website of the corresponding project. But not all of these projects offer precompiled binaries for the platform (operating system / architecture) your webserver is running on. You may have to compile the binaries from the source-code yourself (which is an advanced topic; here is an example of compiling ffmpeg).

There is a special guide dedicated to explaining how to install one of the image toolkits. Installing and configuring the other modules that have external dependencies is very similar and you can basically follow the same procedure for non image toolkit modules.

Absolute filesystem path: Please read the instructions for the netpbm module. All modules that depend on an external program need the path the corresponding binary. Netpbm is a good example on how to find out this path.